Transcript LT AP BIO
Lecture #4 • Chapter 9~ A Musical Journey Through Cellular Respiration Objective: How do organisms produce energy for themselves to do work? Date _________ Principles of Energy Harvest • Catabolic pathway – breaking down molecules to release energy √ Fermentation √Cellular Respiration • • C6H12O6 + 6O2 ---> 6CO2 + 6H2O + Energy (ATP + heat) Products of photosynthesis are the reactants of the cellular respiration Why does ATP store energy? O– O– O – O– O– –O P –O O– P –O O––P OO P––O O– P O– O O O O O • Each Pi group more difficult to add – a lot of stored energy in each bond • most stored in 3rd Pi • ∆G = -7.3 kcal/mole • Close packing of negative Pi groups spring-loaded instability of its P bonds makes ATP an excellent energy donor I think he’s a bit unstable… don’t you? How does ATP transfer energy? O– O– O – –O P –O O– P –O O– P O– O O O • Phosphorylation – when ATP does work, it transfers its 3rd Pi to other molecules • ATP ADP • releases energy – ∆G = -7.3 kcal/mole • it destabilizes the other molecule O– –O P O – + O energy Why is 3rd phosphate like a baaad boyfriend? Exergonic vs Endergonic Reactions SPONTANEOUS NON-SPONTANEOUS What if endergonic reactions need to happen in our body? ATP-coupled reactions • The body couples ATP hydrolysis to endergonic processes by transferring a P to another molecule • The Phosphorylated molecule is less stable (more reactive) • This turns an endergonic reaction to an exergonic (spontaneous) reaction Using ATP to do work? Can’t store ATP too unstable only used in cell that produces it only short term energy storage carbohydrates & fats are long term energy storage Whoa! Pass me the glucose & oxygen! ATP work ADP + P A working muscle recycles over 10 million ATPs per second How do we create ATP? • Cellular Respiration – systematic breakdown of organic molecules (carbs, lipids, proteins, etc.) • Similar to the burning of gasoline in a car Redox reactions – relocation of electrons releases energy which is then used to synthesize ATP • Oxidation-reduction • OIL RIG (adding e- reduces + charge) • Oxidation is e- loss; reduction is e- gain • Reducing agent (oxidized): edonor • Oxidizing agent (reduced): • e- acceptor Oxidizing agent in respiration (electron carrier) • NAD+ (nicotinamide adenine dinucleotide) • Removes electrons from food (series of reactions) • NAD+ is reduced to NADH • NADH carries high energy electrons • Oxygen is the eventual eacceptor Electron transport chains • Electron carrier molecules (membrane proteins) • Shuttles electrons that release energy used to make ATP • Sequence of reactions that prevents energy release in 1 explosive step • Electron route: food---> NADH ---> electron transport chain ---> oxygen Aerobic vs Anaerobic Where does cellular respiration take place? Intermembrane Space Overview of cellular respiration • 4 metabolic stages – Anaerobic respiration 1. Glycolysis – respiration without O2 – in cytosol – Aerobic respiration – respiration using O2 – in mitochondria 2. Pyruvate oxidation 3. Krebs cycle 4. Electron transport chain C6H12O6 + 6O2 6CO2 + 6H2O + ATP (+ heat) Cellular respiration Overview Glycolysis = Sugar + Break down • 1 Glucose 2 pyruvate • Energy investment phase: cell uses ATP to phosphorylate fuel – Glucose G3P • Energy payoff phase: ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH by food oxidation – G3P Pyruvic acid • Net energy yield per glucose molecule: 2 ATP plus 2 NADH; no CO2 is released; occurs aerobically or anaerobically Energy Investment Phase ENZYMES Energy Payoff Phase Substrate-level phosphorylation Oxidation of Pyruvic acid • Each pyruvate is converted into acetyl CoA (begin w/ 2 pyruvate): CO2 is released; NAD+ ---> NADH; • coenzyme A (from B vitamin), makes molecule very reactive ACTIVE TRANSPORT = REQUIRES 2 ATP Kreb’s Cycle • • • • • • If molecular oxygen is present……. From this point, each turn 2 C atoms enter (acetyl CoA) and 2 exit (carbon dioxide) Acetyl CoA combines with Oxaloacetate to form Citric acid (why it is also called citric acid cycle) Oxaloacetate is regenerated (the “cycle”) For each pyruvate that enters: 3 NAD+ reduced to NADH; 1 FAD+ reduced to FADH2 (riboflavin, B vitamin); 1 ATP molecule Totals (2 pyruvates) = 6NADH, 2FADH2, 2 ATP’s, 4 CO2 Electron transport chain • • • • NADH and FADH2 from Glycolysis and Kreb’s are transported to the ETC Cytochromes carry electron carrier molecules (NADH & FADH2) down to oxygen Chemiosmosis: energy coupling mechanism ATP synthase: produces ATP by using the H+ gradient (protonmotive force) pumped into the inner membrane space from the electron transport chain; this enzyme harnesses the flow of H+ back into the matrix to phosphorylate ADP to ATP (oxidative phosphorylation) Review: Cellular Respiration • Glycolysis: 2 ATP (substrate-level phosphorylation) • Kreb’s Cycle: 2 ATP (substrate-level phosphorylation) • Electron transport & oxidative phosphorylation: 2 NADH (glycolysis) = 6ATP 2 NADH (acetyl CoA) = 6ATP 6 NADH (Kreb’s) = 18 ATP 2 FADH2 (Kreb’s) = 4 ATP • 38 TOTAL ATP/glucose – 2 ATP’s used in transporting NADH from glycolysis to mitochondria • Net Gain = 36 ATP’s Pyruvate from cytoplasm Inner + mitochondrial H membrane H+ Intermembrane space Electron transport C system Q NADH Acetyl-CoA 2. Electrons provide energy 1. Electrons are harvested to pump protons and carried to the transport across the system. membrane. - NADH Krebs cycle e- e FADH2 e- 3. Oxygen joins with protons to form water. CO2 2 ATP Mitochondrial matrix H2O 1 O 2 +2 2H+ H+ 32 ATP 4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP. H+ e- O2 H+ ATP synthase Related metabolic processes • Fermentation: alcohol~ pyruvate to ethanol (also creates CO2) – useful for bakers/brewers lactic acid~ pyruvate to lactate • Both create 2 ATP’s • Allow NAD+ to be recycled to glycolysis • Facultative anaerobes (yeast/bacteria)